1. Technical Field
The present invention relates to an electro-optical display, an electrophoretic display, and an electronic device.
2. Related Art
Flat electro-optical displays represented by liquid crystal displays are utilized in various electronic devices, such as OA equipment, information terminals, clocks, and televisions, by taking advantage of the characteristics such as thin profile, lightness in weight, and low power consumption.
Recently, as the electro-optical displays having such characteristics, electrophoretic displays (EPDs) have been remarkably developed. Among the electrophoretic displays, in particular, film-like displays have character visibility and flexibility similar to those of paper media and are therefore known as electronic papers.
A microcapsule-type electrophoretic display (microcapsule-type EPD) is a typical electrophoretic display.
In the microcapsule-type electrophoretic display, microcapsules containing a medium dispersing electrically charged particles are disposed between electrodes, and contrast is obtained by applying a voltage between the electrodes to generate an electric field and thereby changing the distribution of the electrically charged particles.
The electrophoretic display has a characteristic that the electrically charged particles attracted to one side in the microcapsules remain near the electrode by electrostatic force or intermolecular force even if the application of the voltage is stopped, and thereby the displayed image can be retained without consuming power.
Furthermore, in the electrophoretic display, the color (reflected light) of the electrically charged particles or the solvent itself is observed, unlike devices such as liquid crystal displays utilizing transmitted light from backlight or light-emitting devices such as organic EL displays. Therefore, characteristically, the electrophoretic display does not exhibit view angle dependency and is gentle to eyes as in paper to allow being gazed for a long time. In particular, such a characteristic, being a reflective display device in which reflected light from electrically charged particles is observed, is advantageous when it is used under sunlight.
Furthermore, the film-like electrophoretic display has an excellent property, i.e., flexibility. That is, an electrophoretic display having flexibility can be easily realized by using films of, for example, a resin as the two substrates holding the microcapsules therebetween.
However, when the films instead of glass substrates are used as the two substrates holding the microcapsules therebetween, a problem of deterioration of the electrophoretic display due to infiltration of moisture occurs.
In the case of the glass substrates, effect of preventing infiltration of moisture can be sufficiently increased. However, in the case of the films, it is difficult to maintain such effect high. When an electrophoretic display configured using the films is exposed to high temperature and high humidity for a long period of time, deterioration is caused by infiltration of moisture, resulting in a significant decrease in display quality.
In particular, when the display may be used in outdoor environment, deterioration due to changes in temperature and humidity is concerned. Therefore, sufficient moisture protection is required.
JP-A-2005-114820 and JP-A-2005-114822 disclose electrophoretic displays having a structure in which a transparent resin overcoat is laminated on a substrate on a display face side for improving moisture-proof property, and a steam-blocking resin layer is disposed in a gap between the transparent resin overcoat and a substrate on a non-display face side, at the edge surface of the periphery of the displaying surface, for blocking infiltration of moisture.
However, even in the above-mentioned technology, for example, under the environment of a high temperature of about 60° C. and a high humidity of about 90%, moisture infiltrates from the edge surface of the periphery and the back face, which causes degeneration of the electrophoretic material, resulting in deterioration of the display characteristics and retention characteristics.
JP-A-2007-72127 discloses an electrophoretic device whose moisture-resistance property is further improved. This electrophoretic device has a structure in which moisture-proof films are disposed at the top and the bottom of an electrophoretic layer and a moisture-proof resin is further disposed in the periphery of the moisture-proof films, in order to prevent the infiltration of moisture into the electrophoretic layer.
However, in order to ensure a sufficient moisture-proof property by this structure, it is required that the top and bottom moisture-proof films have a high adhesion, in addition to a sufficient moisture-proof property of the material itself.
If the adhesion between the moisture-proof films and the moisture-proof resin is insufficient, moisture infiltrates into the electrophoretic layer using the interfaces as diffusion paths, which may cause a failure that the display quality of the electrophoretic device is deteriorated. Consequently, countermeasures, for example, enlargement of the sealing width, are necessary. The enlargement of the sealing width causes expansion of the periphery of the non-display area, which develops a problem that the merchantability of the electronic paper is significantly decreased.